Asticcacaulis biprosthecum, a member of the Caulobacter group of bacteria, undergoes a complex cell cycle during which several structures (flagella, pili, holdfast, phage receptors) are produced at one pole of the cell, and two prosthecae (cellular stalks) are produced from lateral surfaces of each cell. Thus, three functionally and morphologically distinct regions of the cell envelope are produced and maintained separate from each other, even though the three layers of the cell envelope (plasma membrane, peptidoglycan, outer membrane) are continuous with those of the other two envelope regions. The pole envelope is the only region where specialized polar structures are produced. Prosthecal envelopes are differentiated from two sites of the cell envelope distinct from the pole envelope. Prosthecae appear to be organelles specialized for transport of nutrients from the environment into the cell, and this specialization is reflected in differences in enzymes localized in prosthecae and in the cell proper. In the work proposed here, I will attempt to identify specific roles of components of prosthecal envelopes in membrane transport using purified prosthecae, transport mutants, enzyme assays, and gel electrophoresis. Pleiotropic mutants, lacking prosthecae and differing from wild-type cells in many characteristics, will be studied to determine specific effects of not producing prosthecae. These mutants will also be studied and compared with wild-type cells in attempts to determine mechanisms of control of the complex cell cycle exhibited by these bacteria.